His assumption is based on live-attenuated vaccines. The measles vaccine being one of those. All the early vaccines where like that. The process only requires heat inactivation. So you end up with a dead or almost dead virus, which can't replicate anymore. Your immune system recognizes it as a foreign agent, makes antibodies to tag it for removal.
Today we prefer to immunize with a part of the virus structure, which end up doing the same thing.
Today we prefer to immunize with a part of the virus structure, which end up doing the same thing.